Explosion-proof miniaturized combustible gas sensor

ABSTRACT

The present invention provides an explosion-proof miniaturized combustible gas sensor, comprising: a metal casing having an accommodation space therein; a wire mesh, a vertical surface perpendicular to a side surface where the wire mesh is located and the other side surface opposite thereto being used as a transfer surface of the combustible gas; a heat insulation module embedded in the metal casing; a detection module sensitive to a combustible gas; a compensation module insensitive to a combustible gas and matching the detection module; where the detection module has a higher catalytic combustion activity than the compensation module; a sealant, where a bonding length of the sealant in the accommodation space of the metal casing is used as an effective bonding surface, and the effective bonding surface is perpendicular to the transfer surface. The present invention has the advantages of a miniaturized size, good explosion-proof property and reliable performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a filling under 35 U.S.C. 371 as the National Stageof International Application No. PCT/CN2013/084260 entitledEXPLOSION-PROOF MINIATURIZED COMBUSTIBLE GAS SENSOR and filed Sep. 26,2013, which claims priority to China Patent Application No.201210367286.8 entitled SMALL-SIZE EXPLOSION-PROOF SENSOR FORINFLAMMABLE GAS filed Sep. 28, 2012 with the China State IntellectualProperty Office of the P.R.C. (SIPO) and to China Patent Application No.201220510916.8 entitled EXPLOSION-PROOF TYPE MINIATURIZED COMBUSTIBLEGAS SENSOR filed Sep. 28, 2012 with the China State IntellectualProperty Office of the P.R.C. (SIPO), such that the present applicationalso claims priority to China Patent Application No. 201210367286.8 andChina Patent Application No. 201220510916.8; all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a small and portable combustible gasdetector having a strong explosion-proof capability.

BACKGROUND OF THE INVENTION

In order to prevent explosion of a combustible gas after reaching acertain concentration to ensure production safety, a combustible gasdetecting and alerting device is usually arranged in a factory orfacility wherein a combustible gas is produced and used. A majorconstituent of such combustible gas detecting and alerting device is acombustible gas detector. Current combustible gas detectors mainlyconsist of a gas sensitive element, a gas sensitive element fixingsleeve, a rain cover and a cable entry means.

Currently, a combustible gas detector of such a structure is not securein design, thus, when applied in a combustible gas environment, there isa risk of creating a detonation in the surrounding environment, andproviding a more explosion proof design often cannot be satisfied. Thus,an explosion-proof encapsulation is required. A traditional method toform an explosion-proof encapsulation for a combustible gas detector isto encapsulate a catalytic bead in a stainless steel casing, which has aflame catching and extinguishing sintered sheet, and the end of thecasing is poured with epoxy to be leak-proof. In accordance with thestandard for explosion-proof authentication in Europe and North America,it is required that for any explosion-proof casing, if sealed using asealant, a bonding length between the sealant and the casing in thesealing direction shall be no less than 3 mm. Besides, the design ofsealing with a sealant requires a sufficient size so that the explosionproof effect can be ensured. Thus, the size of a traditional design isusually large, and a small and portable combustible gas detector cannotbe realized.

Usually, measurement means of a combustible gas detector include: athermal conductivity detector, an infrared detector, and catalyticcombustion detection, etc. These detection means mostly adopt the mannerof heat measurement, that is, detecting a combustible gas by influenceon the temperature or heat of a sensitive element caused by flow,infrared absorption or combustion of a combustible gas. However,according to common knowledge, any detection involving heat measurementwill necessarily be influenced by a change in temperature of the ambientenvironment. Thus, a heat-measuring sensor usually requires a referencedetector or a reference element for canceling influence on themeasurement of the detecting element caused by environmental factorssuch as temperature, humidity, pressure, airflow, etc. Obviously, thereference element needs to be infinitely consistent with the detectingelement in term of several factors such as temperature, humidity,pressure and airflow, etc. such that a maximal compensation effect canbe achieved. Unfortunately, the compensation effect of referenceelements in current combustible gas detectors, especially catalyticcombustion or thermal conductivity sensors, are far from ideal due tothe product design and the less advanced production process. That is tosay, currently, combustible gas detectors manufactured by most of themanufacturers still have significant effects of temperature, humidity,pressure and airflow etc. although undergoing compensation by areference element.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an explosion-proofminiaturized combustible gas sensor to solve the problems such aslimitation in the size of a combustible gas detector, difficulty inminiaturization, and poor compensation, etc.

In order to solve the aforesaid problems as well as other problems, thepresent invention provides an explosion-proof miniaturized combustiblegas sensor, comprising: a metal casing having an accommodation spacetherein; a wire mesh provided on a side surface of said metal casing andin connection with said accommodation space for gas exchange such that agas under detection is transferred into said metal casing via said wiremesh; a vertical surface perpendicular to said side surface where thewire mesh is located and the other side surface opposite thereto beingused as a transfer surface of the combustible gas; a heat insulationmodule embedded in the accommodation space of said metal casing; adetection module sensitive to the combustible gas; a compensation moduleinsensitive to the combustible gas and matching said detection module;wherein said detection module has a higher combustible gas detectionsensitivity than said compensation module; a sealant for configuringsaid heat insulation module, detection module and compensation module inthe accommodation space of said metal casing; wherein a bonding lengthof said sealant in said accommodation space of said metal casing is usedas an effective bonding surface, wherein said effective bonding surfaceis perpendicular to said transfer surface of the combustible gas.

Optionally, said detection module comprises: a detection elementassembled in said heat insulation module and a pair of detection pinsconnected to two ends of said detection element respectively andextending via said sealant from a side surface of said metal casing; andsaid compensation module comprises: a compensation element assembled insaid heat insulation module and a pair of compensation pins connected totwo ends of said compensation element respectively and extending viasaid sealant from a side surface of said metal casing.

Optionally, said detection module and said compensation module are fixedin said sensor via a fixing support, or said detection module and saidcompensation module are coupled, nested or locked to each other to fixeach other, thereby being fixed in the sensor.

Optionally, said detection module comprises: a detection elementassembled in said heat insulation module and a pair of detection pinsconnected to two ends of said detection element respectively andextending via said sealant from a side surface of said metal casing; andsaid compensation module comprises: a compensation element assembled insaid heat insulation module and a pair of compensation pins connected totwo ends of said compensation element respectively and extending viasaid sealant from a side surface of said metal casing.

Optionally, the compensation element in said compensation module has alower combustible gas detection sensitivity, or even has no combustiblegas detection sensitivity as compared with the detection element in saiddetection module.

Optionally, the compensation module matching said detection modulecomprises a resistance of said compensation module matching a resistanceof said detection module; in the range of −40° C. to +70° C., where aratio between the resistance of said detection module and the resistanceof said compensation module ranges from 0.975 to 1.013.

Optionally, said detection module further comprises a detection pinframe for supporting said pair of detection pins, said compensationmodule further comprises a compensation pin frame for supporting saidpair of compensation pins.

Optionally, said heat insulation module is composed of a thermalresistance material, where a thermal conductivity coefficient of saidthermal resistance material is smaller than 0.6 w/(m·K), and saidthermal resistance material is of a gas state, a liquid state or a solidstate.

Optionally, a seam allowance slot in contact with said sealant isprovided on an inner wall of said metal casing.

Optionally, a linear expansion coefficient of said sealant is 10⁻⁶in./in./° C.˜10⁻⁵ in./in./° C.

Optionally, a surface of said metal casing includes an opening, and saiddetection module, compensation module and heat insulation module areplaced into the accommodation space of said metal casing via saidopening, thereafter said opening is sealed with said sealant.

The explosion-proof miniaturized combustible gas sensor provided by thepresent invention comprises a metal casing, a wire mesh arranged on saidmetal casing, a heat insulation module embedded in said metal casing, adetection module and a compensation assembled in said heat insulationmodule and a sealant. Such a structure has the following advantages:

1. The transfer surface of the combustible gas is perpendicular to theeffective bonding surface of the sealant such that the bonding lengthrequired by the explosion-proof authentication (e.g. at least 3 mm) doesnot occupy the height of the sensor, thus the overall height of thesensor can be reduced. Besides, since the detection pins and thecompensation pins configured for the detection module and compensationmodule, respectively, extend from a side surface of the metal casing, ascompared with the prior art of the pins extending from the front surfaceor the bottom surface, the overall thickness of the product can bereduced greatly, thereby realizing the miniaturization of the product;furthermore, arranging a heat insulation module in the surrounding ofthe detection module and the compensation module can prevent heat lossdue to a relative big gap between the two modules and the metal casing,in this way, the overall size of the sensor can be further reduced.

2. The present invention provides a detection module sensitive to acombustible gas and a compensation module insensitive to a combustiblegas, and said detection module has a higher combustible gas detectionsensitivity than said compensation module; wherein the so-calledcombustible gas detection sensitivity refers to a change rate of aphysical quantity or a chemical quantity indicating a change of acombustible gas along with a change of concentration of a combustiblegas. Particularly, the detection module and the compensation module aremade into two independent modules and a pairing and matching operationis performed to the two modules during manufacturing, encapsulation isperformed after the matching (e.g. resistance matching to make theresistance values of the two equal or have a very small difference),thereby avoiding the problem of poor compensation and enabling saidcompensation module to compensate influence on a signal of saiddetection module caused by ambient temperature, humidity, pressure andairflow, etc.

3. A linear expansion coefficient of said sealant is 10⁻⁶ in./in./°C.˜10⁻⁵ in./in./° C., which is close to a linear expansion coefficientof stainless steel, thus, even after a one-month-long extreme high andlow temperature cycle as prescribed in the explosion-proofauthentication standard, a sufficient bonding strength between thesealant and the stainless casing can be maintained, which is sufficientto resist the subsequent static hydraulic pressure test of as high as 4MPa.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stereogram of an explosion-proof miniaturized combustiblegas sensor provided by the present invention.

FIG. 2 is a structure breakdown diagram of the explosion-proofminiaturized combustible gas sensor provided by the present invention.

1 Combustible gas concentration detection system 11 Metal casing 13 Wiremesh 15 Heat insulation module 14 Clip 17 Detection module 171 Detectionelement 173 Detection pin 175 Detection pin frame 16 Fixing frame 19Compensation module 191 Compensation element 193 Compensation pin 195Compensation pin frame

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The inventors of the present invention discovered that currentcombustible gas sensors have problems such as limitation in size,difficulty in miniaturization and poor compensation, etc. Thus, theinventors of the present invention have improved the prior art andpropose a novel explosion-proof miniaturized combustible gas sensor,wherein the gas transfer surface is perpendicular to an effectivebonding surface of a sealant, and respective pins extend from a sidesurface of a metal casing, thereby reducing the overall thickness of aproduct and allowing for miniaturization; further, the problem of poorcompensation is avoided by manufacturing a detection module and acompensation module into two independent and matching modules.

The implemention of the present invention is explained with thefollowing specific embodiments. Those skilled in the art can easilylearn other advantages and effects of the present invention through thecontents disclosed in the Description. The present invention can beimplemented or applied through other different specific implementations,and the details in the present Description can be based on differentopinions and applications and modifications and changes can be madewithout deviation from the spirit and principle of the presentinvention.

It should be noted that the structure, proportion and size, etc shown inthe figures of the Description of an explosion-proof miniaturizedcombustible gas sensor according to the present invention are all usedin coordination with the contents disclosed in the Description forreading and understanding of those skilled in the art, but are not usedas limiting conditions under which the present invention can beimplemented and do not have substantive meaning technically. Anymodification to the structure, change in the proportional relation oradjustment of the size, if not affecting the effect of and purposeachieved by the present invention, still fall within the coverage scopeof the technical contents disclosed by the present invention. In themeanwhile, the terms “upper”, “lower”, “left”, “right”, “middle” and “a”used in this Description are only for clarity of description and not forlimiting the scope of implementation of the present invention, thechange or adjustment of the relative relationship thereof withoutchanging the technical content in substance, should be deemed as fallingwithin the implementable scope of the present invention.

FIG. 1 and FIG. 2 show a stereogram and a structure breakdown diagram ofan explosion-proof miniaturized combustible gas sensor provided by thepresent invention respectively. In combination with FIG. 1 and FIG. 2,the explosion-proof miniaturized combustible gas sensor 1 according tothe present invention comprises: a metal casing 11, a wire mesh 13, aheat insulation module 15, a detection module 17, a compensation module19 and a sealant.

Detailed depiction of the aforesaid components is as follows:

The metal casing 11 has an accommodation space therein. In thisembodiment, the metal casing 11 is substantially of a hexahedral boxshape, preferably, it is made of a stainless steel material and has ahigh strength and good heat dissipation performance. A surface of saidmetal casing 11 (e.g. bottom surface) defines an opening, such that saiddetection module 17, compensation module 19 and heat insulation module15, etc. are placed into the accommodation space of said metal casing 11via said opening, thereafter, said opening is sealed with said sealant.Further, an opening is provided on a side surface of the metal casing 11perpendicular to said opening surface (this side surface is referred toas the front surface hereinafter), a wire mesh 13 is sintered at aposition corresponding to said opening. In the present invention, avertical surface perpendicular to said side surface where the wire mesh13 is located and the other side surface opposite thereto serves as atransfer surface of a combustible gas (i.e. T shown in FIG. 1). It canbe seen that the transfer surface of the combustible gas determines theoverall height of the sensor. Wherein, the wire mesh 13 is connected tothe accommodation space of said metal casing 11, which not only has theeffect of allowing ventilation to enable a gas under detection to betransferred into the metal casing 11 via said wire mesh 13 for gasexchange, but also has a further protection effect to prevent a flame ofthe combustible gas to be transferred out to detonate the ambientenvironment. Preferably, the wire mesh 13 is a stainless wire mesh andthe number of holes thereof can be set in accordance with the demand ofthe manufacturing process or the property of the combustible gas.

The heat insulation module 15 is embedded in the accommodation space ofsaid metal casing 11 for heat insulation. In this embodiment, the heatinsulation module 15 can be made by a thermal resistance material (e.g.plastic), and a thermal conductivity coefficient of said thermalresistance material is smaller than 0.6 w/(m·K). Said thermal resistancematerial is of a gas state, a liquid state or a solid state. When saidthermal resistance material is of a solid state, the shape thereof canbe a rod, a block, a sheet or even powder. On the one hand, in order toembed the heat insulation module 15 into the metal casing 11effectively, the present invention further provides a clip 14 for fixingthe heat insulation module 15, specifically, the clip 14 can besubstantially of a Π shape to clamp the heat insulation module 15. Onthe other hand, in order to bond the heat insulation module 15 to themetal casing 11 more closely, a sealant is used (e.g. epoxy pouring)between the heat insulation module 15 and the metal casing 11 to connectthe two and to seal any gap. Furthermore, on the one hand, a flange, apole bolt or an extending portion, etc. can be arranged on an externalwall of the heat insulation module 15 to enhance the bonding degreebetween the heat insulation module 15 and the metal casing 11. On theother hand, a seam allowance slot (not shown in the figure) in contactwith said sealant is specially arranged on the inner wall of the metalcasing 11, such that said sealant is embedded into said seam allowanceslot during sealing to prevent rolling out of the sealant and to enhancethe bonding degree of the sealing. In the present invention, theselected epoxy has a linear expansion coefficient of substantially 10⁻⁶in./in./° C.˜10⁻⁵ in./in./° C., which is sufficiently close to that ofthe material of the heat insulation module 15 and is close to the linearexpansion coefficient of the metal casing 11. In this way, even after aone-month-long extreme high and low temperature cycle (a hightemperature of no lower than 95° C. and a low temperature of −410° C.)as prescribed in the explosion-proof authentication standard, asufficient bonding strength between the sealant and the stainless casingcan be maintained and no crack is generated. Even an explosiveexperiment cannot crack the metal casing 11 and the bonding strength issufficient to resist the subsequent static hydraulic pressure test of ashigh as 4 MPa.

The present invention further provides a detection module 17 sensitiveto a combustible gas and a compensation module 19 insensitive to acombustible gas. In actual application, the detection module 17 and thecompensation module 19 can be fixed in the metal casing 11 through afixing support but is not limited to this, for example, the detectionmodule 17 and the compensation module 19 can also be coupled, nested orlocked to each other to fix each other, thereby being fixed in the metalcasing 11.

The detection module 17 is used to detect a combustible gas, saiddetection module 17 comprises: a detection element 171 assembled in saidheat insulation module 15, a pair of detection pins 173 connected to twoends of said detection element 171 respectively and extending via saidsealant from a side surface of said metal casing 11 and a detection pinframe 175 for supporting the pair of detection pins 173. Thecompensation module 19 is used to compensate influence on a signal ofsaid detection module 17 caused by ambient temperature, humidity,pressure and airflow, etc. The compensation module 19 comprises: acompensation element 191 assembled in said heat insulation module 15, apair of compensation pins 193 connected to two ends of said compensationelement 191 respectively and extending via said sealant from a sidesurface of said metal casing 11 and a compensation pin frame 195 forsupporting the pair of compensation pins 193. Since the detection pins173 and the compensation pins 193 configured on the detection module 17and the compensation module 19 respectively extends from a side surfaceof the metal casing 11, as compared with the prior art of extending froma front surface or bottom surface, this design greatly reduces theoverall thickness of a product and realizes miniaturization of aproduct.

The detection module 17 and the compensation module 19 are substantiallyidentical in structure. A major difference between the two is: thedetection element 171 of said detection module 17 has a highercombustible gas detection sensitivity than the compensation element 191of said compensation module 19, that is, the detection element 171 ofsaid detection module 17 has a relatively higher combustible gasdetection sensitivity, while the compensation element 191 of saidcompensation module 19 has a relatively lower or even no combustible gasdetection sensitivity. Herein, the combustible gas detection sensitivityrefers to a change rate of a physical quantity or a chemical quantityindicating a change of a combustible gas along with a change ofconcentration of a combustible gas. In this embodiment, the detectionelement 171 comprises a noble metal carrying member and a ceramicmaterial wrapping said noble metal carrying member, preferably, saidnoble metal carrying member is a Pt wire coil, said ceramic materialfurther carries a simple substance or a compound sensitive to acombustible gas. The compensation element 191 comprises: a noble metalcarrying member and a ceramic material wrapping said noble metalcarrying member, preferably, said noble metal carrying member is a Ptwire coil. Obviously, the performance of the detection module 17 andperformance of the compensation module 19 must be close enough in termsof thermal conductivity so that the compensation function can berealized. The closer their thermal conductivity performances are, theless the influence of the ambient temperature, humidity, pressure andairflow on the performance of the whole combustible gas sensor. However,the detection component and compensation component in an existingcombustible gas sensor are usually not sufficiently matched due to thedefect in structural design, thus, the existing combustible gas sensorhas a performance far from ideal or requires extra compensation. Theexplosion-proof miniaturized combustible gas sensor provided by thepresent invention, however, takes this into full consideration indesign: the detection module 17 and the compensation module 19 aredesigned as two independent hardware modules, and a pairing and matchingoperation is performed to the two modules in advance duringmanufacturing, upon completion of the matching operation, the twomodules are transferred to the heat insulation module 15 forencapsulation, thereby avoiding the problem of poor compensation andenabling the compensation module 19 to compensate the influence of theambient temperature, humidity, pressure and airflow, etc. on a signal ofthe detection module 17. In actual application, the resistance of thecompensation module 19 matching said detection module 17 means aresistance of said compensation module 19 matching a resistance of saiddetection module 17 (e.g. resistance pairing to make the resistancevalues of the two equal or having a very small difference).Specifically, a ratio between the resistance of said detection module 17and the resistance of said compensation module 19 ranges from 0.93 to1.07, in some embodiments, a ratio between the resistance of saiddetection module 17 and the resistance of said compensation module 19ranges from 0.983 to 1.020. Particularly, in the range of −40° C. to+70° C., a ratio between the resistance of said detection module and theresistance of said compensation module ranges from 0.975 to 1.013.

In order to encapsulate the detection module 17 and the compensationmodule 19 securely in the heat insulation module 15, the presentinvention further provides a fixing frame 16 for fixing the detectionmodule 17 and the compensation module 19. In use, the fixing frame 16 isused as a connection device between the heat insulation module 15 andthe detection module 17 and the compensation module 19. Specifically,one end of the fixing frame 16 is for accommodating the heat insulationmodule 15, and the other end of the fixing frame 16 is for accommodatingthe detection element 171 of said detection module 17 and thecompensation element 191 of said compensation module 19. In actualapplication, said detection module and the compensation module are fixedin said sensor with a fixing support, or the detection module and thecompensation module are coupled, nested or locked to each other to fixeach other, thereby being fixed in the sensor.

The sealant 20 is used to encapsulate said heat insulation module 15,detection module 17 and compensation module 19 in the accommodationspace of said metal casing 11. In the present invention, a bondinglength (corresponding to W shown in FIG. 1) of said sealant 20permeating into the accommodation space of said metal casing 11 is usedas an effective bonding surface, said effective bonding surface isperpendicular to said transfer surface of the combustible gas. In thisway, the effective bonding surface of said sealant and the transfersurface of the combustible gas do not influence each other, and thebonding, length required by the explosion-proof authentication (e.g, atleast 3 mm) does not occupy the height of the sensor (that is, thedistance of the transfer surface of the combustible gas), thereby, theoverall height of a sensor is reduced and the metal casing 11 can bemade into a flat box shape having a size as small as 14 mm*14 mm*5 mm(i.e. L*W*T in FIG. 1), wherein 5 mm is a thickness corresponding to thetransfer surface of said combustible gas in said metal casing 11, whichis much smaller than the height of usually no less than 8 mm of atraditional sensor.

An Example of Actual Application of a Sensor Disclosed by the PresentInvention:

One type of the combustible gas sensor according to the presentinvention is a catalytic combustion combustible gas detector, and itsworking principle is: the detection element 171 in said detection module17 has catalytic combustion activity to methane, while, the compensationelement 191 in said compensation module 19 has no catalytic combustionactivity or a relatively lower catalytic combustion activity to methane.Thus, when a combustible gas appears, the resistance of the detectionelement 171 increases and the resistance of the compensation element 191decreases, remains unchanged or increases by a relatively smalleramplitude. Information about the relative change of the resistances ofthe two can be captured by means of the detection element 171 and theworking element via a Wheatstone bridge, the information is associatedwith a concentration of the methane gas and a concentration value of themethane gas can be obtained through a pre-calibration process.

In summary, an explosion-proof miniaturized combustible gas sensorprovided by the present invention comprises a metal casing, a wire mesharranged on said metal casing, a heat insulation module embedded in saidmetal casing, a detection module and a compensation assembled in saidheat insulation module and a sealant. Such a structure has the followingadvantages:

1. The transfer surface of the combustible gas is perpendicular to theeffective bonding surface of the sealant such that the bonding lengthrequired by the explosion-proof authentication (e.g. at least 3 mm) doesnot occupy the height of the sensor, in this way, the overall height ofthe sensor can be reduced. Besides, since the detection pins and thecompensation pins configured for the detection module and compensationmodule respectively extend from a side surface of the metal casing, ascompared with the prior art of the pins extending from a front surfaceor bottom surface, the overall thickness of the product can be reducedgreatly, thereby realizing the miniaturization of the product;furthermore, arranging a heat insulation module in the surrounding ofthe detection module and the compensation module can prevent heat lossdue to a relative big gap between the two modules and the metal casing,in this way, the overall size of the sensor can be further reduced.

2. The present invention provides a detection module sensitive to acombustible gas and a compensation module insensitive to a combustiblegas, and said detection module has a higher combustible gas detectionsensitivity than said compensation module. Particularly, the detectionmodule and the compensation module are made into two independent modulesand a pairing and matching operation is performed to the two modulesduring manufacturing, encapsulation is performed after the matching(e.g. resistance matching to make the resistance values of the two equalor have a very small difference), thereby avoiding the problem of poorcompensation and enabling said compensation module to compensateinfluence on a signal of said detection module caused by ambienttemperature, humidity, pressure and airflow, etc.

3. A linear expansion coefficient of said selected sealant is 10⁻⁶in./in./° C.˜10⁻⁵ in./in./° C., which is close to a linear expansioncoefficient of stainless steel, thus, even after a one-month-longextreme high and low temperature cycle as prescribed in theexplosion-proof authentication standard, a sufficient bonding strengthbetween the sealant and the stainless casing can be maintained, which issufficient to resist the subsequent static hydraulic pressure test of ashigh as 4 MPa.

The above embodiments are only for illustratively explaining theprinciple and effect of the present invention, rather than limiting thepresent invention. Any skilled person in the art can makemodification(s) to the above embodiment without deviating from thespirit and scope of the present invention. Thus, the scope of protectionof the present invention shall be defined as those listed in the Claims.

The invention claimed is:
 1. An explosion-proof miniaturized combustiblegas sensor comprising: a metal casing having an accommodation spacetherein: a wire mesh provided on a front vertical surface of said metalcasing and in connection with said accommodation space for gas exchangesuch that a gas under detection is transferred into said metal casingvia said wire mesh; a pair of vertical surfaces perpendicular to saidfront vertical surface where the wire mesh is located and a backvertical surface in a direction opposite the front vertical surface thedirection being aligned as a transport direction of the combustible gas;a detection module sensitive to the combustible gas; a compensationmodule insensitive to the combustible gas, wherein said detection moduleand said compensation module have the same structure; wherein saiddetection module has a higher combustible gas detection sensitivity thansaid compensation module; a seam allowance slot around an opening in ahorizontal bottom surface of the metal casing located perpendicular tothe pair of vertical surfaces; a heat insulation module clamped to thedetection module in the accommodation space of said metal casing; asealant for embedding said heat insulation module, detection module andcompensation module in the accommodation space and the seam allowanceslot of said metal casing; wherein a bonding length of said sealant withsaid metal casing and the seam allowance slot in said accommodationspace of said metal casing is used as a bonding surface, wherein saidbonding surface is perpendicular to said transport direction of thecombustible gas.
 2. The explosion-proof miniaturized combustible gassensor according to claim 1, wherein said detection module and saidcompensation module are fixed in said sensor via a fixing support, orsaid detection module and said compensation module are coupled, nestedor locked to each other to fix each other, thereby being fixed in thesensor.
 3. The explosion-proof miniaturized combustible gas sensoraccording to claim 1, wherein the detection module comprises: adetection element assembled in the heat insulation module and a pair ofdetection pins connected to two ends of the detection elementrespectively and extending via the sealant from a bottom surface of themetal casing; and wherein the compensation module comprises: acompensation element assembled in the heat insulation module and a pairof compensation pins connected to two ends of the compensation elementrespectively and extending via the sealant from a bottom surface of themetal casing.
 4. The explosion-proof miniaturized combustible gas sensoraccording to claim 3, wherein the compensation element in saidcompensation module has a relatively lower combustible gas detectionsensitivity, or even has no combustible gas detection sensitivity ascompared with the detection element in said detection module.
 5. Theexplosion-proof miniaturized combustible gas sensor according to claim 1wherein the compensation module matching said detection module comprisesa resistance of said compensation module matching a resistance of saiddetection module; in the range of −40° C. to +70° C., a ratio betweenthe resistance of said detection module and the resistance of saidcompensation module ranges from 0.975 to 1.013.
 6. The explosion-proofminiaturized combustible gas sensor according to claim 3, wherein saiddetection module further comprises a detection pin frame for supportingsaid pair of detection pins, said compensation module further comprisesa compensation pin frame for supporting said pair of compensation pins.7. The explosion-proof miniaturized combustible gas sensor according toclaim 1, wherein said heat insulation module is composed of a thermalresistance material, a thermal conductivity coefficient of said thermalresistance material is smaller than 0.6 w/(m·K), and said thermalresistance material is of a gas state, a liquid state or a solid state.8. The explosion-proof miniaturized combustible gas sensor according toclaim 1, wherein a seam allowance slot in contact with said sealant isprovided on an inner wall of said metal casing.
 9. The explosion-proofminiaturized combustible gas sensor according to claim 1, wherein alinear expansion coefficient of said sealant is 10⁻⁶ in./in./° C.˜10⁻⁵in./in./° C.
 10. The explosion-proof miniaturized combustible gas sensoraccording to claim 1, wherein a surface of said metal casing comprisesan opening, and said detection module, compensation module and heatinsulation module are placed into the accommodation space of said metalcasing via said opening, thereafter said opening is sealed with saidsealant.
 11. An explosion-proof miniaturized combustible gas sensorcomprising: a metal casing having an accommodation space therein: a wiremesh provided on a front vertical surface of the metal casing and inconnection with the accommodation space for gas exchange such that a gasunder detection is transferred into the metal casing via the wire mesh;a pair of vertical surfaces perpendicular to the front vertical surfacewhere the wire mesh is located and back vertical surface oppositethereto; a detection module sensitive to the combustible gas; acompensation module insensitive to the combustible gas, wherein thedetection module and the compensation module have the same structure;wherein the wire mesh is aligned with the detection module and thecompensation module in the transport direction; a seam allowance slotaround an opening in a horizontal bottom surface of the metal casinglocated perpendicular to the pair of vertical surfaces; a heatinsulation module clamped to the detection module in the accommodationspace of said metal casing; a sealant for embedding the heat insulationmodule, detection module and compensation module in the accommodationspace and the seam allowance slot of the metal casing; wherein a bondinglength of said sealant with said metal casing and the seam allowance insaid accommodation space of said metal casing is used as a bondingsurface, wherein said bonding surface is aligned perpendicular to saidtransport direction of the combustible gas.
 12. The explosion-proofminiaturized combustible gas sensor according to claim 11, wherein thedetection module and the compensation module are fixed in the sensor viaa fixing support, or the detection module and the compensation moduleare coupled, nested or locked to each other to fix each other, therebybeing fixed in the sensor.
 13. The explosion-proof miniaturizedcombustible gas sensor according to claim 1, wherein the detectionmodule comprises: a detection element assembled in the heat insulationmodule and a pair of detection pins connected to two ends of thedetection element respectively and extending via the sealant from abottom surface of the metal casing; and wherein the compensation modulecomprises: a compensation element assembled in the heat insulationmodule and a pair of compensation pins connected to two ends of thecompensation element respectively and extending via the sealant from abottom surface of the metal casing.
 14. The explosion-proof miniaturizedcombustible gas sensor according to claim 13, wherein the compensationelement in the compensation module has a relatively lower combustiblegas detection sensitivity, or even has no combustible gas detectionsensitivity as compared with the detection element in the detectionmodule.
 15. The explosion-proof miniaturized combustible gas sensoraccording to claim 13, wherein the detection module further comprises adetection pin frame for supporting the pair of detection pins, thecompensation module further comprises a compensation pin frame forsupporting the pair of compensation pins.
 16. The explosion-proofminiaturized combustible gas sensor according to claim 11 wherein thecompensation module matching said detection module comprises aresistance of said compensation module matching a resistance of saiddetection module; in the range of −40° C. to +70° C., a ratio betweenthe resistance of said detection module and the resistance of saidcompensation module ranges from 0.975 to 1.013.
 17. The explosion-proofminiaturized combustible gas sensor according to claim 11, wherein theheat insulation module is composed of a thermal resistance material, athermal conductivity coefficient of the thermal resistance material issmaller than 0.6 W/(m·K), and the thermal resistance material is of agas state, a liquid state or a solid state.
 18. The explosion-proofminiaturized combustible gas sensor according to claim 11, wherein aseam allowance slot in contact with the sealant is provided on an innerwall of the metal casing.
 19. The explosion-proof miniaturizedcombustible gas sensor according to claim 11, wherein a linear expansioncoefficient of the sealant is 10⁻⁶ in./in./° C.˜10⁻⁵ in./in./° C. 20.The explosion-proof miniaturized combustible gas sensor according toclaim 11, wherein a surface of the metal casing comprises an opening,and the detection module, compensation module and heat insulation moduleare placed into the accommodation space of the metal casing via theopening, thereafter the opening is sealed with the sealant.